Much work has been done over the years to convert heavy hydrocarbonaceous materials to more valuable lighter boiling products. Various thermal processes which have resulted from such work include visbreaking; catalytic hydroconversion, in both a slurry and ebullating bed; fluid coking; and delayed coking.
Of particular interest in the practice of the present invention is fluid coking. In fluid coking, a heavy hydrocarbonaceous chargestock, such as a vacuum residuum, is fed to a coking zone comprised of a fluidized bed of hot solid particles, usually coke particles, sometimes also referred to as seed coke. The heavy hydrocarbonaceous material is reacted in the coking zone, resulting in conversion products which include a vapor fraction and coke, which coke is deposited on the surface of the seed coke particles. A portion of the coked-seed particles is sent to a heating zone which is maintained at a temperature higher than that of the coking zone. Some of the coke is burned off in the heating zone. Hot seed particles from the heating zone are returned to the coking zone as regenerated seed particles, which serves as the primary heat source for the coking zone. In some fluid coking processes, a portion of hot coke from the heating zone is circulated back and forth to a gasification zone which is maintained at a temperature greater than that of the heating zone. In the gasifier, substantially all of the remaining coke on the coked seed particles is burned, or gasified, off. Several U.S. patents which teach fluid coking, with or without an integrated gasification zone, are U.S. Pat. Nos. 3,726,791; 4,203,759; 4,213,848; and 4,269,696; all of which are incorporated herein by reference.
Many process modifications have been made over the years in an attempt to achieve higher liquid yields. For example, U.S. Pat. No. 4,378,288 discloses a method for increasing coker distillate yield in a thermal coking process by adding small amounts of a free radical inhibitor.
Notwithstanding any advantages the foregoing processes may have, there is still a need in the art for process variations which can increase liquid yields.